CENTRIFUGAL CHILLERS SINGLE COMPRESSOR
PART 2 PRODUCTS
2.4 CHILLER COMPONENTS A. Compressor
1. Unit shall have a single-stage hermetic centrifugal compressor. Casing design shall ensure major wearing parts, main bearings, and thrust bearings are accessible for maintenance and replacement. The lubrication system shall protect machine during coast down period resulting from a loss of electrical power.
2. The impeller shall be statically and dynamically balanced. The compressor shall be vibration tested and not exceed a level of 0.14 IPS.
3. Movable inlet guide vanes actuated by an internal oil pressure driven piston shall accomplish unloading. Compressors using an unloading system that requires penetrations through the compressor housing for linkages that must be lubricated and adjusted are acceptable provided the manufacturer provides a five-year inspection agreement consisting of semi-annual inspection, lubrication, and annual change out of any compressor seals. A statement of inclusion must accompany any quotations.
4. If the compressor is not equipped with guide vanes for each stage and movable discharge diffusers, then furnish hot gas bypass and select chillers at 5% lower kW/ton than specified to compensate for bypass inefficiency at low loads.
B. Lubrication System: The compressor shall have an independent lubrication system to provide lubrication to all parts requiring oil. Provide a heater in the oil sump to maintain oil at sufficient temperature to minimize affinity of refrigerant, and a thermostatically controlled water-cooled oil cooler. Coolers located inside the evaporator or condenser are not acceptable due to inaccessibility. A positive displacement oil pump shall be powered through the unit control transformer.
C. Refrigerant Evaporator and Condenser:
1. Evaporator and condenser shall be of the shell-and-tube type, designed, constructed, tested and stamped according to the requirements of the ASME Code, Section VIII.
Regardless of the operating pressure, the refrigerant side of each vessel will bear the ASME stamp indicating compliance with the code and indicating a test pressure of
6. A self-metering and adjustable thermal expansion valve shall control refrigerant flow to the evaporator. Fixed orifice devices or float controls with hot gas bypass are not acceptable because of inefficient control at low load conditions. The liquid line shall have a moisture indicating sight glass.
7. The evaporator and condenser shall be separate shells. A single shell containing both vessel functions is not acceptable because of the possibility of internal leaks.
8. Reseating type spring loaded pressure relief valves according to ASHRAE-15 safety code shall be furnished. The evaporator shall be provided with single or multiple valves. The condenser shall be provided with dual relief valves equipped with a transfer valve so one valve can be removed for testing or replacement without loss of refrigerant or removal of refrigerant from the vessel. Rupture disks are not acceptable.
9. The evaporator, suction line, and any other component or part of a component subject to condensing moisture shall be insulated with UL recognized 3/4 inch closed cell insulation. All joints and seams shall be carefully sealed to form a vapor barrier.
10. Provide factory mounted water pressure differential switches on each vessel to prevent unit operation with no flow.
D. Prime Mover: Squirrel cage induction motor of the hermetic type of sufficient size to efficiently fulfill compressor horsepower requirements. Motor shall be liquid refrigerant cooled with internal thermal overload protection devices embedded in the winding of each phase. Motor shall be compatible with the starting method specified hereinafter. If the Contractor chooses to provided an open drive motor or compressor, verify in the submittal that the scheduled chiller room ventilation system will accommodate the additional heat and maintain the equipment room at design indoor temperature based on 95qF outdoor ambient ventilation air available.
If additional cooling is required, manufacturer shall be responsible for the installation, wiring and controls of a cooling system. Chiller selection shall compensate for tonnage and efficiency loss to make certain the owner is not penalized.
E. Motor Starter:
load shall be based on the total heat rejection to the atmosphere from the refrigeration units.
3. For open motor units, an oil reservoir shall collect any oil and refrigerant that leaks past the seal. A float device shall be provided to open when the reservoir is full, directing the refrigerant/oil mixture back into the compressor housing.
Manufacturer shall warrant the shaft seal, reservoir, and float valve system against leakage of oil and refrigerant to the outside of the refrigerating unit for a period of 5 years from the initial start-up including parts and labor to replace a defective seal and any refrigerant required to trim the charge original specifications.
4. The starter must comply with the requirements of Section 1.2.
5. All controllers are to be continuous duty AC magnetic type constructed according to NEMA standards for Industrial Controls and Systems (ICS) and capable of carrying the specified current on a continuous basis. The starter shall be:
Autotransformer - The autotransformer starter shall be of the closed transition type and equipped with multiple taps for 80%, 65%, 50%, and set up for the 65% tap. A clearly marked timer shall be adjustable from 0 to 30 seconds.
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Wye-Delta Closed Transition - The wye contactor shall be capable of handling 33% of the delta locked rotor current and be equipped with properly sized resistors to provide a smooth transition. The resistors shall be protected with a transition resistor protector, tripping in a maximum of two seconds, locking out the starter, and shall be manually reset. A clearly marked transition timer shall be adjustable from 0 to 30 seconds.
-- Or --
Solid-State Reduced Voltage - Starter shall be furnished with silicon controlled rectifiers
directly operate the main motor contactors. The MCRs shall constitute the only means of energizing the motor contacts.
8. The main contactors shall have a normally open and a normally closed auxiliary contact rated at 125VA pilot duty at 115 VAC. An additional set of normally open contacts shall be provided for each MCR.
9. There shall be electronic overloads in each phase set at 107% of the rated load amps of each motor. Overloads shall be manual reset and shall de-energize the main contactors when the overcurrent occurs. The overloads shall be adjustable and selected for mid-range. Overloads shall be adjusted for a locked rotor trip time of 8 seconds at full voltage and must trip in 60 seconds or less at reduced voltage (33%
of delta LRA).
10. Each starter shall have a current transformer and adjustable voltage dropping resistor(s) to supply a 5.0 VAC signal at full load to the unit control panels.
11. Each starter shall be equipped with a line-to-115 VAC control transformer, fused in both the primary and secondary, to supply power to the control panels, oil heaters and oil pumps.
12. Each starter shall include the following protective devices:
a) Phase failure and reversal protection -OR-
E Variable Frequency Drive
1. The chiller shall be equipped with a Variable Frequency Drive (VFD) to automatically regulate compressor speed in response to cooling load and compressor pressure lift. The chiller control shall coordinate compressor speed and guide vane position to optimize chiller efficiency.
2. A digital regulator shall provide V/Hz control.
3. The VFD shall have 110% continuous overload of continuous amp rating with no time limit, PWM (pulse width modulated) output, IGBT (insulated gate bipolar transistors) power technology, full power rating at 2kHz, DC bus inductor (choke), and wireless construction.
4. Units 240 amps and below shall be air-cooled, units above 241 amps shall be water-
1. The display shall have a minimum of 160-character liquid crystal display and be backlit with a light emitting diode. Messages shall be in plain English. Coded two or three character displays are not acceptable.
2. The following information shall be available on the display with simple entry on the keypad:
a) Entering and leaving chilled and condenser water temperatures b) Evaporator, suction, discharge, condenser, and liquid temperatures c) Suction and discharge superheat
d) Liquid subcooling, evaporator and condenser approach temperatures e) Evaporator, condenser, and compressor lift pressures
f) Oil feed and sump temperatures
g) Oil pump discharge and oil differential pressure h) Motor amps and amps as a percent of rated load amps
i) Hours of operation and number of starts, time of last start and stop j) Chilled water setpoint and reset temperature setpoint
k) Amp limit for manual and remote
l) History for last 8 faults with date and time plus critical sensor values m) Unit status; start-up and shutdown sequence, operational status
3. The microprocessor shall either unload or shut down the compressor during an abnormal condition. At a minimum the following safeties shall be incorporated in the control system:
a) High and low discharge pressure b) Low evaporator pressure c) High discharge temperature
d) Chilled or condenser water pump failure e) No evaporator or condenser water flow f) High or low oil feed temperature g) Low oil differential pressure
h) High motor temperature, low motor current
6. The controller shall be able to reset chilled water temperature by controlling return chilled water temperature or from a remote 4-20 mA DC signal. The amount of reset shall be adjustable.
7. Programmable load ramping shall be provided to prevent the unit from operating at full load during pulldown if desired.
8. A time clock shall be incorporated to allow daily timed starts and stops and to allow for holidays and weekends.
9. The control system shall have automatic restart after a power failure and not require a battery backup for memory continuity. A battery shall be provided for the time clock only.
10. The controller shall be capable of starting and stopping chilled and condenser water pumps. It shall also be capable of four-step control of cooling tower fans and provide an analog output for a tower bypass valve.
11. The microprocessor shall be capable of communicating to other units or a PC using a twisted pair communication interface of RS-232 (100 feet) or RS-422/485 (5000 feet) or with a 9600 baud modem.